package blog.network;

import java.io.*;

public class Base64 {

    static final char[] charTab =
        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
            .toCharArray();

    public static String encode(byte[] data) {
        return encode(data, 0, data.length, null).toString();
    }

    /** Encodes the part of the given byte array denoted by start and
    len to the Base64 format.  The encoded data is appended to the
    given StringBuffer. If no StringBuffer is given, a new one is
    created automatically. The StringBuffer is the return value of
    this method. */

    public static StringBuffer encode(
        byte[] data,
        int start,
        int len,
        StringBuffer buf) {

        if (buf == null)
            buf = new StringBuffer(data.length * 3 / 2);

        int end = len - 3;
        int i = start;
        int n = 0;

        while (i <= end) {
            int d =
                ((((int) data[i]) & 0x0ff) << 16)
                    | ((((int) data[i + 1]) & 0x0ff) << 8)
                    | (((int) data[i + 2]) & 0x0ff);

            buf.append(charTab[(d >> 18) & 63]);
            buf.append(charTab[(d >> 12) & 63]);
            buf.append(charTab[(d >> 6) & 63]);
            buf.append(charTab[d & 63]);

            i += 3;

            if (n++ >= 14) {
                n = 0;
                buf.append("\r\n");
            }
        }

        if (i == start + len - 2) {
            int d =
                ((((int) data[i]) & 0x0ff) << 16)
                    | ((((int) data[i + 1]) & 255) << 8);

            buf.append(charTab[(d >> 18) & 63]);
            buf.append(charTab[(d >> 12) & 63]);
            buf.append(charTab[(d >> 6) & 63]);
            buf.append("=");
        }
        else if (i == start + len - 1) {
            int d = (((int) data[i]) & 0x0ff) << 16;

            buf.append(charTab[(d >> 18) & 63]);
            buf.append(charTab[(d >> 12) & 63]);
            buf.append("==");
        }

        return buf;
    }

    static int decode(char c) {
        if (c >= 'A' && c <= 'Z')
            return ((int) c) - 65;
        else if (c >= 'a' && c <= 'z')
            return ((int) c) - 97 + 26;
        else if (c >= '0' && c <= '9')
            return ((int) c) - 48 + 26 + 26;
        else
            switch (c) {
                case '+' :
                    return 62;
                case '/' :
                    return 63;
                case '=' :
                    return 0;
                default :
                    throw new RuntimeException(
                        "unexpected code: " + c);
            }
    }

    /** Decodes the given Base64 encoded String to a new byte array. 
    The byte array holding the decoded data is returned. */

    public static byte[] decode(String s) {

        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        try {
            decode(s, bos);
        }
        catch (IOException e) {
            throw new RuntimeException();
        }
        return bos.toByteArray();
    }

    public static void decode(String s, OutputStream os)
        throws IOException {
        int i = 0;

        int len = s.length();

        while (true) {
            while (i < len && s.charAt(i) <= ' ')
                i++;

            if (i == len)
                break;

            int tri =
                (decode(s.charAt(i)) << 18)
                    + (decode(s.charAt(i + 1)) << 12)
                    + (decode(s.charAt(i + 2)) << 6)
                    + (decode(s.charAt(i + 3)));

            os.write((tri >> 16) & 255);
            if (s.charAt(i + 2) == '=')
                break;
            os.write((tri >> 8) & 255);
            if (s.charAt(i + 3) == '=')
                break;
            os.write(tri & 255);

            i += 4;
        }
    }
}
